Temperature control device



s. EslqN TEMPERATHE CONTROL DEVICE` Filed oct. e', 1932 ma F M vin 5amuel EsKn, MM.; His Attorneg.

Patented Dee. 17, 1935 samuel askin, Rubin, china, mmm u Gm# eral'Electric Company, a corporation of New York Application october s, 1932, semi No. sans (ci. zia-zo) 6 Claims.

My invention relates to temperature control devices, more particularly to devices for controlling an electric circuit in accordance with temperature changes, and has for its object the provision of an improved device of this char-l acter.

Morejspeciiically, my invention relates to tempera'ture-control devices for electric heating pads and the like, although it has application to various other types of electrically heated devices.

One object c.' my invention is the provision of l i improved temperature control means arranged so that a relativeLv large number of preselected temperatures can be maintained in the heating pad.

In carrying my.invention into effect in one form thereof, I provide the pad with a thermo- Vstat arranged to control the heating circuit. of

the heating padresponsively to the pad temperature.' In order to control the temperature lmaintained in the pad, I provide an auxiliary source of heat for supplying heat to the thermostat in addition to that which it receives from the pad. This auxiliary source of heat is controlled independently of the operation of the thermostat by suitable conti-ol means, such as an adjustable resistance element.,

.In the operation of my control device, the thermostat is adjusted to open the pad heating circuit at a predetermined temperature. The

Ydifference in the temperature maintained in the pad andthat for which the thermostat is adjusted to open .the 'heating circuit is proportional'l to the quantity of heat supplied by the auxiliary source. The-greater the quantity of heat supplied by this source, 4the lower will be the temperature held in the pad; and conversely, the smaller the quantity of heat supplied by .the auxiliary source, the higher will be the temperature maintained in the pad.-

. For a more complete understanding of my invention reference should be had to the accompanying drawing in which Fig. 1 is a plan view of anelectric heating pad provided with a temperature control device arranged in accordance with my invention; Fig. 2 is a vertical sectional view of a thermostat used in my temperature control device; Fig. 3 is a plan view of a control memberl for my control device and heating pad of Fig. 1; and Fig. '4 is a diagrammatic view illustrating the heating pan and temperature control device of Fig. 1. l

Referring to the drawing, I have shown my invention in one form as applied to an electric heating pad. It is to be understood, however,

used, and since these that .my invention has application to various other types of electrically heated devices.

The heatingpad may have any suitable 'construction, and may be formed of cloth or anyv other suitable material. 5

'Ihe heating pad is provided with a heating element I arranged in a series of convolutions Il distributed overa comparatively large area of the pad, as shown in Fig. 1. Preferably, the convolutions will be formed of a pair of resistance conductors arranged in parallel relation, as clearly shown in Fig. 1, the extreme ends of the conductors being electrically connected. The resistance conductor Il may be formed of any suitable material, such as nickel-chromium alloy. l5

.The resistance wire may be insulated in any suitable manner, the details ofl disclosed. l

The details of constructions of the heating pad and the means for insulating the resistance conv 'ductor i0 have not been shown in detail. since any preferred well-known constructions may be features form no part of which are noty my invention.

' The heating element Il of the pad is ener- 25 gized from a suitable source' of electrical supply I2, the element being connected `with the sup- Y ply source by means of a suitable twin supply 'l conductor i3. A suitable control Vdevice Il is inserted in the twin supply conductor I3, one A- function of thel control device being to control the connections between the supply source and the heating circuit of the pad.

"The heating circuit of the padis'controlled by means of a pair of thermostats I6 and I8 36 which are connected in series relation with each other and with the resistance element Il at one end thereof, as clearly shown in Figs. 1 and 4. Whilethe thermostats are connected at oneend of the heating elementprovided for the pad, they 40 are located at ydiiferent portions of the pad, as shown in Fig. 1, so as to respond to the temperatures ofdifferent portions of the pad. Thus,

-it will be observed by reference to Fig. 1 that the thermostats Il I I are located on opposite sides of a, longitudinal center line of the pad. It will be understood that these thermostats will function to maintain the same pad temperature but that two have been provided for the purpose of increasing the safety of operation of .the pad.

Ejach thermostat comprises a bimetallic bar I1 made of two strips of metal having dissimilar temperature coeilicients of expansion, such as brass and steel, the strips being securely brazed or welded together lengthwise. The thermostat is rigidly secured at one end to a frame or sup,

port i8 by means of clamping studs or rivets 2li rial, such as mica.

The unsecuredl end of the bimetallic bar Il is free to move laterally in response to changes in temperature. This movable end of the bar care ries a contact 22 which may be formed integrally with the bar by bending the end of the bar back upon itself, as clearly shown in Fig. 2. This contact cooperates with a fixed contact 23 carried by a contact member 24. The member 63 preferably will be formed integrally with the trame I3 and may be formed' as' a tongue ont from the metal forming the frame. The contact arm 263 may be moved relative to the frame, but normally will be held in a position xed with relation to the frame by means oi an adjustable abutment l or stop 25, shown as a set screw. As shown, the frame I6 is provided at its end adjacent the end of the contact arm 24 with` a portion E6 bent upon itself in the form of a U so as to define a seat Afor receiving the adjusting screw 25. The adjusting screw 25 is provided with a conical head 2l which engages a portion 2d of the contact arm 2t inclined to the general plane oi the arm insuch manner that when the screw is turned the position of the contact arm and hence oitheilxed contact 23 is adjusted.

Each thermostat I5, `I 6 is provided with a termin nal 30 that is in electrical contact with the bi metallic bar Il, and with a terminal 3l that is in electrical contact with the frame I8.

The frame I8, the bimetallic bar Il, the adjusting screw 25 and the terminals 30 and 3|, are ar ranged as a unitary structure. This unitary structure is supported ina tubular casing 32. This casing may be formed by any suitable material having a relatively goodheat conductivity, such BS Coppel'.

The terminal so of the thermostat is is elec minal 3| of the thermostat I5 is electrically connected with one of the conductors I3a orc the twin supply conductor I3 through a conductor 34a.

By reason of these connections, it will be observed, vthat the bimetallic bars Il of the two thermostats are connected in series with each` other and with the heating element I0.

In order to control the operation of the thermostat to maintain preselected temperatures injthe heating pad, I provide each thermostat with an auxiliary heating element'35 arranged luther- 'mal relation withthe bimetallic bar I1 oi' thethermostat. Referring more particularly to Fig. 2, git will be observed that the heating element 35 is wound in coil form upon the tubular support 32. The heater coils will be formed of any sitable material, such as a nickel-chromium alloy. lThe turns ofthe heater coils are electrically insulated in any suitablemanner, as by an insulating varnish. Each coil is provided with a pair of terminals 36a.

The heater coils 35 of the thermostats are electrically connected in series with each other, and are energized from the supply source I2. The electrical energy supplied to the heater coils 35 is controlled by means of a. suitable resistance g yelement 3S which preferably will be of the carbon pile type. Thus, for example, the resistance elenient may be formed of alternately arranged carbon and metal discs 31 and 38 secured ytogetherin any suitable manner. lo

Preferably, the control device I4 controlling the connections between the heating pad and the supply source i3, and the rheostat 36 controlling the heaters 35 will be incorporated into a unitary structure, as shown in Fig. 3. As shown in this g- 15 ure, the control device I4 comprises a control lever it pivotally mounted in a suitable insulating housing di and cooperating with the carbon pile rhecstat 36 and with a suitable contact 42. The pivotally mounted lever 40 is provided with a pair 20 of spring-'like contacts t3 and 3 which cooperate respectively with the rheostat 36 and with the contact d2. The contact 42, as shown in Figs. 3 and 4, is electrically connected to one ofV theleads 03h o.l the' supply conductor I3 from the supply 25 source I2.

One endvoi the rheostat 36, the right hand end, as viewed in Figs. 3 and 4, is electrically connected with one terminal of the heating coil 35 of the rheostat IE by means ofla conductor 44. 30 The other terminal oi' this heating coil is electrically connected with one terminal of the heating coil 35 oi the thermostat I6 by means' of a conductor d5. The other terminal of this thermostat is electrically connected to the other lead I3a 35 of thesupply conductor AI3vby. means of a. conductor l and the conductor 34a. The contact going connections the heating element I0 isconnected in series with the two bimetallic elements I'I of the thermostats I5 and I6 and with the supply source, and that the heating coils 35 of the 45 two thermostats are electrically connected in se- 4 ries with the supply source through the adjustable rheostat 36.

In order to control the energy input to the heating elements 35, it is merely necessary to adjust 50 the position of the control lever 46. It will be observed that while the arm 40 is being adjusted,

- the circuit will be maintained through the heating element I0 by the contact 42 with which'the contact arm has a sliding engagement. 55 In lthe operation of my temperature control def vice, it will be understood that the bimetallic bars I1 will receive heat both from the heating pad and from the auxiliary heating coils 36 provided `for the thermostats. 60

However, when the lever '40 isin its extreme right` hand position at the point indicated 0 in Fig. l, whichvis the off` position of the arm, the

-circuits through the .heating coil I0 of the pad and of the'thermostat heating coils l3I5 are de- 65 energized. As the arm 40 is moved from this position toward th'e position marked L, which 'indicates the low heat position of the contact arm,

it will engage the rheostat 36 so as to complete an energizing circuit for the heating elements 35.*70 When thecontact ann arrives at its low heat position L", it will engage the contact 42 and complete the heating circuit 'through the pad 4resistance elementl. In this position of the arm 40, very little resistance will be included in series with y 9,094,153 the heating elements and so, the elements will l assuming that the thermostatsare set to operate toopen the heating circuit vil at 180 P., it is obvious that the pad temperaturewill not attain 180 F. when the thermostats'thus operate, but will have a temperature considerably less than 1ao.`

The value of the pad temperature at the instant .the thermostats function to open the heating circuit depends to a great extent upon the resistance of the pad heating circuit, that of the elements 35 and the effective resistance of the rheostat 30.

In a specific example, assuming that the reslstance of the element I0 be 200 ohms, that of the rheostat 3B to be 12,000 ohms with an effective resistance of 3.000 ohms ir the low heat position, and that the combined resistances of the heating elements 35 to be 6,000 ohms, each having a resistance of 3,000 ohms, then in thelow heat position, the pad will attain a temperature ofsubstantially 110 F., assuming, as before, that the thermostats are set to cut on the heat at 180 F. In this position of-the lever Il, each heater coil 30 will deliver approximately .5 watts to its thermostat. It will be understood that as long as the lever 40 is in its low heat position "L", a temperature of substantially 110 l". will be maintained in the pad. l That is, when the pad attains a temperature of 110 F. adjacent either thermostat i5, I0 the thermostat will function to cut oil the heat, and then to reapply the heat when the pad cools to a temperature below 1101". In this manner the thermostats function to maintain a substantially constant temperature in the pad. g 4

'If the control arm 40 be moved in a counter clockwise direction, more and more effective resistance of the rheostat 30 will `be inserted in the energizing circuit of the heating elements and as a result, these elements will impart less and lessheat to the thermostat bars il. In other words, more 'and more heat must come from the pad to each thermostat in order to actuate it to open the heating circuit of the pad. vAs before, assuming that each thermostat is adjusted to operate at a temperature of 180 F., the temperature maintained in the pad will gradually be increased from 110 F. to this valueas the arm 4l is moved toward the left.

When the arm 40 is moved to the extreme lefthand end of the rheostat all of the effective resistance will be inserted in the heating circuit of the thermostats, and as a result the wattage supplied by each heater l! will be reduced from .5

watts, its low heat value, to approximately .3.

watts in the specific example given above. When the arm 40 reaches its high heat position, 'indicatedI-I -in Fig. 1, it will have disengaged or moved oil of the carbon pile 3l which operation will deenergize the auxiliary heaters All of the heat necessary-to actuate the thermostats to open the pad lheating circuit must come from the pad itself. In other words, the padmust operate I .at a temperature of 180 F. before the thermovstats will function to disconnect the heating element I0. In order to reduce the temperature maintained in the pad, it is merely necessary to adjust the arm 40 to a lower heat position.

' the thermostats it is necessary to adjust the position of the fixed contacts 23 by turning the ad- Justing screws 25. It will be understood that this adjustment usually will be made merely for factory purposes, and that when once thethermostat 1s is adjusted it will be unnecessary to change its adjustment in the normal operation of the pad.

It will be observed that I have provided a temperature control device whereby a very great number of temperatures within a wide range can 20 be maintained in the heating pad il, and that any one of these temperatures can be secured merely ,by adjusting the position of the control arm Il.

While I have shown a particular embodiment ofimy invention, it will be understood, of course, gs that I do not wish to be limited thereto since'many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modications as. fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent ofthe United States is:

1. In anelectrlcally heated device, electrical heating means for said device,.an energizing circuit for said heating means, a thermostat in $6 thermal relation with said device so as to receive heat directly therefrom arranged to control said energizing circuit of.v said heating means responsively to the temperature of said device so as to control said-heating means to hold a sub- 40 stantially constant temperature in said device, an auxiliary heating element in thermal relation n with said thermostat arranged to apply heat directly thereto in addition to that received directly from-said device, a second energizing circuit d5 for said auxiliary heating device independent of said first energizingv circuit for said heating means so that the energization of said auxiliary heating device is uniniluenced by the operation of said thermostat controlling said ilrst energizing cir-'5G cuit, and means connected in said second energizing circuit controlling the energy input to said auxiliary heating element to vary its heating effect on said thermostat and thereby vary the temperature setting of said thermostat to hold u different preselected temperatures in said device. 2. A temperature control device for electric heating `pads and the like comprising a switch 'Y in the heating circuit of ysaid pad, a thermostat responsive to the temperature of said pad controlling said switch, a heating element in thermal relation with said thermostat, a circuit for said heating element independent of the pad heating circuit and an adjustable resistance in said eircuit for controlling the energy input to said heating element.

3. In an electricheating pad, a heating circuit for said pad, a switch in said heating circuit, a thermostat responsive to the temperature of said 7 pad controlling said heating circuit, a heating lement in thermal relation with said thermostat, an energizing circuit for said heating element, an adjustable resistance in said circuit for controlling the energy input to said heating element and 1| a common operating member for said switch and said resistance arranged to close and open said switch to energize and deenergize said heating circuit and to adjust said resistance While said heating circuit is energized so as to control the energy input to said heating element.

4. In an electric heating pad, a heating circuit for said pad, a set of electrical supply conductors for said pad, a thermostat in said pad controlling said heating circuit responsively to the tempera ture of said pad, an auxiliary heating element in said pad in thermal relation with said thermostat arranged to apply heat directly thereto in additionto that received .from said pad, a second set of. electrical supply conductors for said auxiliary heating element, means incorporating both sets of said supply conductors into a single supply cord and a common control device in said cord for said sets of conductors including a switch controlling said first set of conductors to open and close said heating circuit, a resistance connected in said second set of conductors to control the energize.- tion of said auxiliary heating element and a common control member for operating said switch and for controlling the effective amount oi said resistance connected in the circuit of said auX- iliary heating element.

5. A temperature control system for electric heating pads and the like provided with a body member and a heating circuit in said body member comprising a set of electrical supply conductors for said heating circuit, a switch controlling said conductors, a thermostat lin said body member responsive to the temperature aoaawe thereof arranged to control said heating circuit, a heating element in said pad in thermal relation With said thermostat, a second set of electrical supply conductors for said heating element, a common supply cord for both of said sets of supvply conductors for said heating circuit and said heating element, an adjustable resistance connected in said second set or" supplyconductors for controlling said heating element, and a common control member in said cord for said switch and said resistance arranged to close and open said switch to energize and deenergize said heating circuit and to adjust said resistance while said heating circuit is energized so as to control the energy input to said heating element.

6. In an electric heating pad, a heating circuit for said pad, a switch in said heating circuit, a thermostat responsive to the temperature ci said pad controlling said heating circuit, a heating element in thermal relation with said thermo- 

